1. Field of the Invention
This invention relates to a silicone composition for the treatment of glass fibers, which produces electrical insulating materials with excellent flame retardancy, electrical characteristics, mechanical strength and transparency when woven glass fiber fabrics and glass sleeves are coated or impregnated with the compositions.
2. Description of the Prior Art
Certain silicone rubber dispersion varnish compositions with excellent flame retardancy and pliability were recently proposed for treating glass fiber products useful as electrical insulating materials. For example, a silicone rubber composition described in Kokai Japanese Patent Number: Sho 52(1977)-63961, was prepared from a vinyl containing organopolysiloxane, and an organohydrogenpolysiloxane, a metal salt of an organic acid, a platinum catalyst, and fume silica filler using diphenylsilanediol as an agent for hydrophobic treatment of the silica filler. The prepared silicone rubber composition was dissolved or dispersed in an organic solvent to obtain a varnish solution in an attempt to improve flame retardancy of the varnish film. A silicone rubber composition described in Kokai Japanese Patent No. Sho 52(1977)-63495, was prepared from a vinyl containing diorganopolysiloxane, an organohydrogenpolysiloxane, fumed silica filler, hexaorganodisilazane, a platinum catalyst and optionally a silicone resin. The hexaorganodisilazane is used as an agent for hydrophobic treatment of a silica filler. The silicone rubber composition thus prepared was dissolved or dispersed in an organic solvent to obtain a varnish solution in an attempt to improve transparency of the varnish film. This varnish is useful for treating glass fiber and such treated products are said to have excellent electrical insulation properties and flame retardancy.
However, these prior art compositions are unsatisfactory in terms of transparency, workability, and bath life of the varnish solution. In the case using diphenylsilanediol as an agent for hydrophobic treatment of a silica filler, there are the drawbacks that transparency of the film and the flow characteristics of the varnish solution are impaired significantly due to the differences in compatibility and refractive index between the silicone polymer and diphenylsilanediol. In the case using hexamethyldisilazane as a surface treating agent for a silica filler, the bath life of the varnish solution is significantly reduced due to the presence of trace amounts of ammonia from the decomposition residue of hexamethyldisilazane in spite of the fact that transparency of the film can be improved due to close compatibility and similarity of refractive index between the silicone polymer and the surface of the trimethylsilylated silica. That is, a structure is formed during the storage period resulting in the drawback that the bath gels completely and loses its flowability.